On the bionomics and pathogenicity of Oedemerid beetles : Studies on poisonous beetle, I

<p>Very little attention has been paid to the human dermatitis caused by Oedemerid beetles. As the results of the author's investigation presented here, however, it has been elucidated that the disease were fairly common in various districts of Japan. In this paper the author intended to list up the species of Oedemerid beetles which cause dermatitis. There were involved some species newly reported as the cause. The mechanism of the occurence of dermatitis and the clinical symptoms were also traced experimentally. The main results are summarized as follows : 1. Except for the previously known species in Japan represented by Xanthochroa atriceps, X. waterhousei, X. hilleri and X. ainu, three more species were found to cause dermatitis in nature, namely Nacerdes melanura, Eobia cinereipennis and Eobia chinensis ambusta. Records of cases of dermatitis caused by Oedemerids in the world were briefly reviewed (Table 1). 2. By means of the patch-test, 24 species of the Japanese Oedemerids belonging to 12 genera were tested for the presence of the dermatitis-producing substances (Table 2). In case of fresh specimens, the materials were crushed and applied on the skin of forearm. In case of dried specimens, an extraction was made wth chloroform and after evaporating chloroform it was applied in a similar way mixed with vaselin. Thus the species, such as Anoncodes sambucea, Xanthochrca wadai, X. katoi, X. caudata, X. luteipennis, X. konoi, X. osawai, X. deformis, Chrysarthia viatica, Oedemerina concolor, Oedemeronia manicata and O. lucidicollis, were proved to cause dermatitis under experimental conditions. The toxic substance was identified as cantharidin in the succeeding experiments and the details of results were presented in another paper by the author and his colleague in this volume (pp.200-201). 3. Skin lesions caused by Oedemerid beetles were described in detail. After a few hours of the application of the toxic substance, bullae or vesicles of characteristic nature appear rather suddenly. They vary in shape and size, and also in number. They are light yellow to yellowish brown in colour, tense and convex as a rule, and apt to rupture by friction. The bullae are surrounded by a very narrow inflammatory halo and accompanied by some pain and itch. It usually takes a week or a little more before the lesions are completely healed, but, when the bullae are broken, pain becomes more intensive and cure is much delayed. They leave a well-defined pigmentation for a long period. 4. Various experiments were made to clarify the modes of occurence of dermatitis by contact with the beetles. Xanthochroa waterhousei, one of the most common species as the cause, was selected as the material in the experiment. The beetle never causes skin lesions when allowed to walk freely on the bare arm. However, it secretes the toxic fluid from the costae of elytra and the anterior and posterior margin of pronotum when irritated by pressure, such as compression with hand, or even when simply swept away with a finger. The toxic substance is contained in practically every part of beetle, as the lesions can be produced experimentally by rubbing the skin with isolated head, antenna, prothorax, meso-metathorax, elytron, wing, leg and abdomen respectively. Even the eggs or larvae were found to contain the toxin, and caused dermatitis by crushing them on the skin. 5. The practical significances of the Oedemerid beetles as the cause of human dermatitis differ in accordance with the species, and depend both on physiological and ecological characters of beetles. Members of the genera Anoncodina, Ezonacerda, Ditylus, Chrysarthia, Asclera, Oedemerina and Oedemernia may be of little significance since they are diurnal in activity and usually stay on wild plants and rarely come in contact with human life. Members of the genera Nacerdes, Xanthochrca, Eobia and Oncomerella are of epidemiological importance as they are</p><p>(View PDF for the rest of the abstract.)</p>